CBSE Blockchain Cryptography Fundamentals 4

Question 1

Schnorr signatures offer which advantage over ECDSA that is particularly valuable for multi-signature schemes on blockchains?

Accepted Answer

Multiple signatures can be aggregated into a single compact signature

Answer

Schnorr signatures support linear aggregation, allowing multiple signers to combine their signatures into one, reducing on-chain storage and improving privacy in multi-sig schemes.

Question 2

In the context of blockchain key management, a BIP-39 mnemonic phrase encodes entropy as:

Accepted Answer

A list of 12–24 words derived from a standardized wordlist that encodes the wallet seed

Answer

BIP-39 converts entropy (128–256 bits) into 12–24 human-readable words from a 2048-word list, making wallet backup more reliable and user-friendly.

Question 3

Which cryptographic technique underpins Confidential Transactions in blockchains like Monero, hiding transaction amounts while still allowing miners to verify no coins are created from nothing?

Accepted Answer

Pedersen commitments

Answer

Pedersen commitments are homomorphic, allowing miners to verify that inputs equal outputs without knowing the actual values, hiding transaction amounts cryptographically.

Question 4

An attacker performs a 51% attack and attempts to double-spend. Which cryptographic property of SHA-256 makes rewriting deep blockchain history computationally prohibitive even with majority hash power?

Accepted Answer

Pre-image resistance forces the attacker to redo all proof-of-work for every block in the rewritten chain

Answer

Pre-image resistance means there is no shortcut to find a nonce satisfying the target — the attacker must brute-force redo every block's proof-of-work for the rewritten chain.

Question 5

What is the primary cryptographic security concern with using the same public/private key pair for both signing and encryption operations?

Accepted Answer

Cross-protocol attacks can use ciphertexts to forge signatures or vice versa

Answer

Using the same key for signing and encryption can enable cross-protocol attacks where an adversary submits crafted ciphertexts as signing inputs to extract key material.

(CBSE) Certified Blockchain Security Expert Practice Test

(CBSE) Certified Blockchain Security Expert Practice Test

CBSE Blockchain Cryptography Fundamentals 4